The invention relates to a torque limiting coupling, especially for drives of or driving agricultural machinery. The coupling includes a first coupling part with apertures which extend parallel to an axis of rotation. The apertures are uniformly distributed on a rolling circle. A second coupling part is rotatable around the axis of rotation relative to the first coupling part. The second coupling part is axially fixed. The second coupling part has torque transmitting recesses at its end face opposed to the first exit end of the apertures. The recesses are arranged to match the arrangement of the apertures. A switching ring is rotatably arranged around the axis of rotation relative to the first coupling part. The second coupling part includes freewheeling recesses in its end face opposed to the second exit end of the apertures. The freewheeling recesses are arranged to match the arrangement of the rolling circle and the distribution of the apertures. However, in the torque transmitting position, the freewheeling apertures are held so as to be displaced in the circumferential direction relative to the apertures. Torque transmitting balls are axially adjustably received in the apertures. The balls engage the torque transmitting recesses in the torque transmitting position and the freewheeling recesses in the freewheeling position. A spring axially acts on the switching ring. The spring supports the switching ring against any adjustment away from the apertures.
DE 31 51 485 C1 describes a torque limiting coupling. To secure the two coupling parts relative to one another in the torque transmitting position, a plurality of securing pins are provided. The pins are arranged on the circumference of the first coupling part and are spring-loaded in the axial direction. The pins engage recesses of the switching ring so that the switching ring cannot change its position relative to the first coupling part. After overloading has occurred, the two coupling parts can reach a torque transmitting position relative to one another which differs from the original one. However, with some applications, such a difference can be disadvantageous. In the case of land machinery where certain parts of the machine performs different functions of the machine, the parts are adjusted to one another in such a way all movements are synchronous.
DT 25 26 212 A1 describes a torque limiting coupling which includes torque transmitting balls arranged in a cage positioned between two planar faces of two coupling parts. One part is the driving part and the other one the driven part. The surfaces of the two coupling parts positioned opposite the cage are provided with circumferentially distributed recesses. The recesses correspond to the balls held in the cage. The recesses are engaged by the balls for torque transmitting purposes if the coupling is in the connected position. A spring loads the axially adjustable coupling part. If the torque limited by the spring is exceeded, the adjustable coupling part is moved against the force of the spring. Thus, the balls are able to leave the recesses and enter other recesses of the driven coupling part. In the case of overloading, the coupling parts are supported by supporting balls which are arranged on a smaller radius than the first balls. In the connected condition, the supporting balls engage recesses in the two coupling parts. The recesses for the supporting balls are distributed in such a way that the supporting balls and the balls simultaneously engage their associated recesses. For re-connecting the coupling, the cage is deliberately rotationally adjusted by a tool. Thus, it is possible to find a position in which the supporting balls and the further balls are able to engage their associated recesses. Since there are three circumferentially distributed supporting balls with the same pitch, the supporting balls and the three balls, provided for torque transmitting purposes, are all able to engage at a rotational angle of 120.degree. of the coupling parts relative to one another.
DE 37 27 484 A1 describes an improved version of the torque limiting coupling proposed in DE 25 26 212 A1. Here, stops are provided which simplify reconnection of the coupling.
GB 21 33 093 A describes a torque limiting coupling where balls are used for torque transmitting purposes. The balls engage opposed recesses in the two coupling parts and leave the recesses against the force of a spring when one coupling part is axially adjusted. Three uniformly circumferentially distributed balls and recesses enable the balls to engage in three different circumferential positions of the two coupling parts relative to one another. The further balls arranged on the smaller rotational diameter remain in constant engagement with the second coupling part and a driving element. However, the balls enable axial adjustment of the two relative to one another. The balls are a substitute for teeth.